The present invention generally relates to node apparatuses, and more particularly to a node apparatus of a communication network employing a multi-conjunction architecture.
Conventionally, as communication networks applicable to local area networks (LANs), there are a network employing a carrier sense multiple access with collision detection (CSMA/CD) method using coaxial cables for buses as typified by an Ethernet (registered trademark), an optic star shaped network using optical fibers for buses, and an optic loop shaped network employing a time-division multiple access (TDMA) method. The network using optical fibers is less affected by noise caused by external electro-magnetic waves when compared to the network using coaxial cables.
In the network using buses such as the Ethernet, a fault in a node apparatus will not cause the entire system to go down, but the entire system will go down when a node apparatus oscillates or a cable breaks. In the case of the star shaped network, the entire system will go down when a fault occurs in a central part of the network. Furthermore, in the case of the loop shaped network, there is a possibility of the entire system going down when a fault occurs in a node apparatus or a link. It is possible to provide the loop in duplicate, but it would make the construction of the node apparatus extremely complex.
On the other hand, as communication networks applicable to multi-media communications, there are a carrier sense multiple access (CSMA) base-band LAN typified by the Ethernet, a broad-band LAN, and a TDMA base-band LAN in combination with a digital private branch exchange (DPBX).
The CSMA base-band LAN is suited for the communication of information which has a short packet length such as data information and text information and is generated in a burst. However, in the case of the multi-media communication where the message length is not limited and in the case where the data is generated continuously, a collision of data occurs frequently. For this reason, it is impossible to obtain a high throughput, and the CSMA base-band LAN is not best suited for the multi-media communication.
The broad-band LAN is not best suited for the multi-media communication due to the following reasons. In other words, the capacity of the broadband LAN is insufficient, there is a limit to the expansion of the system, and the system is expensive.
On the other hand, the TDMA base-band LAN is more suited for the multi-media communication than the CSMA base-band LAN and the broad-band LAN. However, there is also a limit to the expansion of the system, and the system is expensive. Especially when the TDMA base-band LAN is applied to the multi-media communication, the cost of the system becomes substantial.
Accordingly, the present inventor has previously proposed a lattice communication network analogous to nerve cells of a living body in a U.S. Pat. No. 4,516,272. According to this proposed lattice network, each node apparatus has a plurality of input and output channels and is used as a communication control element, and such node apparatuses are coupled in a multi-conjunction to constitute the lattice network. Each node apparatus transfers one of incoming digital signals according to a first-come-first-served logic (hereinafter referred to as a first-come-first-output logic).
The proposed lattice network has a large degree of freedom of network topology because of the multi-conjunction architecture. Thus, the survivability of data is high. In other words, even when a fault occurs in a path of the network, it is possible to carry out the communication through other paths. Furthermore, it is possible to select optimum paths for the communication because each node apparatus transfers the incoming digital signals according to the first-come-first-output logic.
However, when it takes time to select the optimum paths and fix a communication path which is to be used and a large number of long message packets are to be transmitted, it is only possible to obtain a throughput which is in the range of the throughput obtainable in the CSMA base-band LAN. Therefore, the communication is not completely carried out in the full duplex. In addition, when the returning of a responding signal is slow, the detection of failure of the communication becomes slow, and it is impossible to effectively carry out the backoff such as controlling a re-transmission. Accordingly, there is a demand to realize a full duplex communication also in a multi-channel system in which a node apparatus simultaneously couples to a plurality of channels.
On the other hand, when the contention method is employed in setting a link, the collision of the message packets prevents the realization of a high throughput. The probability that the collision is generated is proportional to a maximum network propagation delay time, that is, the time it takes for a message packet sent from a sending (source) terminal device to reach a farthermost terminal device.
According to the proposed lattice network, the setting of the link is determined by the contention method using the first-come-first-output logic. Because the lattice network has the multi-conjunction architecture, the maximum network propagation delay time is intrinsically short. In addition, even when the collision is generated, the communication is completed if the destination terminal device is located inside a boundary determined by the collision, and a plurality of communications may be completed when the collision occurs. However, in order to sufficiently improve the throughput, it is desirable that the maximum network propagation delay time is further shortened.
The function of setting the link for the input channel to which the signal is first received is realized at a high speed by wired logic. But when the link is set after detecting the incoming message packet, there is a possibility that a front portion of the message packet will drop out even when the wired logic is used since a circuit delay is inevitably introduced by the detection. The dropout of the front portion of the message packet occurs at each node apparatus, and the dropout is accumulated every time the message packet passes through a node apparatus. This accumulation of the dropout is one of the causes limiting the further reduction of the maximum network propagation delay time.
In the case of the half duplex communication, the input channels are coupled to all of the output channels in an initial state of the line. According to a system previously proposed in a Japanese Patent Application No. 60-170429, an input channel which receives an input signal first is detected when input signals are received by the input channels, and the other input channels are disconnected from the output channels. As a result, it is possible to prevent the front portion of the message packet from dropping out by an amount corresponding to the time it takes to determine the input channel which receives the input signal first received according to the first-come-first-output logic.
However, according to the previously proposed lattice networks, a responding signal is restricted from being transferred before the transfer of a sending signal is completed, as may be seen from a Japanese Patent Application No. 60-170427, for example. In other words, although the full duplex communication is basically possible, no responding signal such as acknowledge or not acknowledge is transferred while the first message packet is being transferred. Accordingly, the communication is not completely carried out in the full duplex. In addition, when the returning of the responding signal is slow, the detection of failure of the communication becomes slow, and it is impossible to effectively carry out the backoff such as controlling the re-transmission. In a multi-channel system in which a node apparatus simultaneously couples to a plurality of channels, the algorithm of each node apparatus becomes complex and the construction of the node apparatus becomes extremely complex.
In order to obtain a high data survivability in the lattice network, it is important that the effects of faults are minimized and the trouble shooting is carried out quickly. There are three major faults, namely, a first fault caused by the fault in the node apparatus itself, a second fault in the sending path, and a third fault in a receiving path. In the proposed lattice networks, the probability that the first and second faults will occur is extremely small.
However, when the third fault occurs, a serious problem occurs when the first sending signal sent from the node apparatus reaches a destination terminal device. In other words, the first sending signal reaches the destination terminal device because there is no fault in the sending path between the node apparatus and the destination terminal device, but because there is a fault in the receiving path between the destination terminal device and the node apparatus, the responding signal from the destination terminal device such as the acknowledge signal cannot be sent back to the sending (source) terminal device. The lattice network will then re-transmit the first sending signal, but the same sending path will be selected because it is the optimum path and there is no fault in the selected optimum path. As a result, the destination terminal device is again unable to send back the responding signal to the node apparatus because of the fault in the receiving path. The proposed lattice networks are unable to obviate this problem.